docs: def _var_uint_field_handler(handler, ctx):
      """Handler co-routine for variable unsigned integer fields that.
  
      Invokes the given ``handler`` function with the read field and context,
      then immediately yields to the resulting co-routine.
      """
      _, self = yield
      queue = ctx.queue
      value = 0
      while True:
          if len(queue) == 0:
              # We don't know when the field ends, so read at least one byte.
              yield ctx.read_data_transition(1, self)
          octet = queue.read_byte()
          value <<= _VAR_INT_VALUE_BITS
          value |= octet & _VAR_INT_VALUE_MASK
          if octet & _VAR_INT_SIGNAL_MASK:
              break
      yield ctx.immediate_transition(handler(value, ctx))